Which Of The Following Animals Are Considered An Amniote?

Amniotes Definition

Amniotes are vertebrate organisms which accept a fetal tissue known as the amnion. The amnion is a membrane derived from fetal tissue which surrounds and protects the fetus. The amnion can be institute within the egg, every bit in lizards and birds, or the amnion can only enclose the fetus within the uterus.

Amniotes include most of the vertebrates, excluding fish and amphibians. Fish and amphibians are anamniotes, meaning "without an amnion". The eggs of these species are often laid in water, which protects them from beingness damaged or squished. Almost amniotes, by contrast, are terrestrial and require the amnion to protect the developing fetus nether the weight of gravity. The but exceptions to this are the whales, which live an entirely aquatic life. They developed an amnion before their ancestors returned to the bounding main. Some marine turtles also similar in the sea, but return to land to lay their eggs, making the amnion necessary.

Characteristics of Amniotes

All amniotes have three membranes surrounding the fetus of one offspring. These membranes are the amnion, or protective layer, the acme chorion layer, and the waste product-arresting allantois. These layers tin can be seen in the image of a chicken egg, beneath.

While amniotes share a number of other characteristics in general (existence vertebrates, tetrapods, etc.), they all adult from a common ancestor which developed the amnion character. The amnion is seen within egg-laying species, such every bit birds and reptiles, equally well as in mammals. While man eggs have lost the shell, in many means they are identical to chicken eggs as they develop within the uterus.

Animals Considered Amniotes

Sauropsid Amniotes

There are ii main divisions of amniotes, the sauropsid amniotes and the synapsid amniotes. The sauropsid amniotes include the reptiles and birds. Formally, this constitutes many different groups, but the sauropsid amniotes share many derived characteristics which separate them from the synapsids. The two groups evolved around the same time, from a mutual antecedent which was likely not terrestrial.

This ways that both the synapsids and sauropsids had to adjust to the new terrestrial environment in a number of different ways. These differences are reflected in the heart, lungs, and kidneys mainly. In sauropsids, at that place will ordinarily be found faveolar lungs, which differ from the lungs of the synapsids. Faveolar lungs have small chambers which open to a mutual space. The heart of sauropsids lacks a permanently divided ventricle. While some sauropsids (turtles and crocodiles) have developed hearts that are about 4 chambered, they are not the synapsid heart with a physical separation between the ventricles.

The sauropsid amniotes also excrete waste differently than the synapsids. Sauropsids typically excrete uric acid (the white paste in bird poop). This substance precipitates out of the urine in the cloaca, where much of the water can be reabsorbed. This makes uric acid a more h2o-efficient way of excreting nitrogenous wastes, versus the synapsid method. Sauropsids include turtles, lizards, crocodiles, and birds. Typically, they lay eggs although there are some exceptions.

Synapsid Amniotes

The synapsid amniotes do things slightly dissimilar, since they separated from the sauropsids millions of years ago. The synapsid strategy for expelling waste, for example, is typically all urea. Urea can be concentrated in the synapsid kidney, and excreted with small bits of water. While this may non be as water-efficient as uric acrid, it is much more efficient than excreting straight ammonia, which is what fish and amphibians typically do.

The heart of synapsids is 4-chambered, with a well-divers sectionalisation between ventricles. This improves the efficiency of oxygenating the claret, by insuring separate paths for claret going to and from the heart. Synapsids adult different lungs than the sauropsids. The synapsid lung is an aveolar lung. Instead of small pockets from a central chamber, the aveolar lung has many branches of trachea, each which ends at an aveolar sac.

In that location are simply 3 extant groups of synapsids, all of which are mammals. While all of these amniotes however have amniotic sacs, they likewise have very dissimilar methods of reproducing. The monotremes, like the platypus, withal lay eggs in nests. When the young hatch, they feed them milk from glands in their skin, like all other mammals. The marsupials correspond a median betwixt the monotremes and the placental mammals. They develop their young within a uterus, just the immature are built-in at an extremely early on age. They must climb along the mother into the marsupial pouch, where they tin can feed on milk for the residue of development.

The placental mammals represent the rest of the synapsid amniotes. These animals use a placenta, or oxygen and food passing maternal membrane, to feed and nourish offspring within the womb. At birth, offspring of these animals are the largest of all amniotes comparatively. Even so, placental mammals also have fewer offspring compared to sauropsid amniotes.

Development of the Amniotes

Amniotes likely emerged as many of the offset terrestrial animals were venturing onto state. The much unlike terrestrial environment is likely what drove the divisions between the ii main groups of amniotes. This likely occurred in the Devonian menses, around 400 million years agone. Since and so, the two groups accept evolved considerable differences in their anatomy and physiology, as discussed above. At the time, the new terrestrial surroundings provided a number of new niches for the animals to make full, which likewise diversified them significantly.

Below is an organism which could have been a common antecedent of modernistic amniotes. This is a parieasaur, a cow-sized organism from the Devonian flow. This large reptile-looking organism probable had archaic lungs, heart, and kidneys. It also probable had an amnion, making information technology one of the first amniotes.

Quiz

References

• Feldhamer, M. A., Drickamer, 50. C., Vessey, S. H., Merritt, J. F., & Krajewski, C. (2007). Mammology: Adaptation, Diversity, Ecology (tertiary ed.). Baltimore: The Johns Hopkins University Printing.
• Pough, F. H., Janis, C. Grand., & Heiser, J. B. (2009). Vertebrate Life. Boston: Pearson Benjamin Cummings.
• Widmaier, E. P., Raff, H., & Strang, Yard. T. (2008). Vander's Human being Physiology: The Mechanisms of Body Function (11th ed.). Boston: McGraw-Loma Higher Pedagogy.

Source: https://biologydictionary.net/amniote/

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